Noxious weed threatens the biggest wildlife migration on the planet

24 November 2010 | News story

The Serengeti - Masai Mara ecosystem in Africa, which hosts the largest wildlife migration known to man, is under attack from a noxious weed from Central America, commonly known as feverfew (Parthenium hysterophorus). If left unchecked it could threaten the continued migration of millions of animals across the plains every year, including 1.5 million wildebeest, 500,000 Thomson’s gazelle and 200,000 zebra.

The Serengeti - Mara ecosystem hosts approximately 70 large mammal species and some 500 different bird species in highly diverse habitats ranging from riverine forests, swamps, grasslands and woodlands. Researchers from CABI Africa and IUCN, based in Nairobi, Kenya, found the weed, parthenium, during a recent survey, growing along parts of the Mara River and along some dirt tracks in the Masai-Mara National Reserve.

“Although this weed may look benign to most people it probably poses one of the most serious threats to the ecosystem, which is already under threat from illegal hunting, land conversion, fencing, disease and uncontrolled fires,” says Arne Witt, Invasive Species Coordinator, CABI Africa. “Research suggests that conditions in the Serengeti are highly suitable for this weed so we should all be very concerned.”

Parthenium has gained notoriety in Australia, India and Ethiopia where it was accidentally introduced with what many would consider disastrous consequences. The weed, which can grow from seed to maturity in 4-6 weeks and has an ability to produce 10,000–25,000 seeds, is known to be allelopathic, which in layman’s language means that it produces chemicals which inhibit the growth of other plants. This means that if it invades natural pasture it can reduce the amount of available forage to such an extent that carrying capacities of grazing animals can be reduced by up to 90%. If allowed to grow without any weeding it can reduce yields of crops, such as sorghum, by up to 97%. It is also toxic, which means that animals will not eat it unless they are starving or stressed, with fatal consequences. This weed also has impacts on human health – many people who come into direct contact with the plant can develop severe skin allergies (dermatitis) and pollen production by the plant can result in respiratory problems.

The implications for wildlife conservation in the Serengeti ecosystem are potentially extremely serious. The movement of thousands of grazing animals means that the grasslands are often highly disturbed, making it easier for parthenium to invade. The displacement of palatable species means that, in time, the available food for wildebeest, zebra, gazelle and the pastoralists livestock will rapidly diminish.

“Unless action is taken immediately to eradicate known infestations in the Masai-Mara National Reserve it is not unrealistic to expect a drastic reduction in wildlife populations in the long term as the parthenium population rapidly expands as an invading species,” says Geoffrey Howard, IUCN’s Global Invasive Species Programme Coordinator. “It is therefore possible for a little green plant to transform one of the greatest spectacles on earth.”

“However, we can stop the invasion in its tracks and protect this national and global treasure for our children's grand-children if we all work together in support of the Kenyan government and national institutions which have indicated, based on their pronouncements at CABI’s 100 year celebrations held at Nairobi National Park, that they are committed to managing invasive species in Kenya,” says Arne Witt.